The invention relates to a cooling system for cooling the stator and/or the rotor of a generator, and to a method for cooling the stator and/or the rotor of a generator.
A hydrogen-cooled synchronous generator with a water-cooled stator winding is described in the book xe2x80x9cSynchronmaschinenxe2x80x9d [Synchronous Machines], AEG Telefunken Handbxc3xccher, Volume 12, Berlin 1970, on page 53. Generators with a water-cooled stator winding require a water loop. It comprises pumps for circulating the primary cooling water, return coolers and filters which ensure that the stator winding is not soiled, and an expansion vessel which is fitted on top on the machine. Fine filters and an ion exchanger for preparing the water are connected in the shunt circuit to this main circuit. Since the cooling water must be fed to the stator winding via insulating hoses, a small fraction of hydrogen can diffuse via them from the machine interior into the water circuit. This hydrogen fraction is given the opportunity of degassing from the water in the not entirely filled expansion vessel. It is led to the outside via a pressure control valve and a gas meter.
German patent application DE 22 22 487 describes a device for removing non-absorbed gases in liquids in the case of liquid-filled electric machines. In accordance with FIGS. 1 and 2 of that document, two concepts are applied for a cooling circuit. On the one hand, a coolant compensating container via which coolant is supplemented is connected to the cooling circuit via a spur line. In that compensating container which is disposed outside of the cooling circuit, a degassing container through which the entire coolant flow passes is connected into the cooling circuit. Outgassing of the coolant occurs in the degassing container. The gases are discharged to the outside. In accordance with the other concept, the compensating container for the coolant is integrated into a shunt circuit connected in parallel with the main cooling circuit. In this case, a smaller coolant flow of the shunt circuit passes continuously through the compensating container which serves simultaneously as a degassing container.
A cooling water circuit for a water-cooled electric machine is described with the aid of FIG. 5 in Siemens-Zeitschrift [Siemens Journal], Vol. 41, 1967, issue 10, pages 838-39. The cooling water must have a low electric conductivity for reasons of insulation. For this reason, chemical filters or ion exchangers, which continuously reduce the ion concentration in the cooling water, are connected into the cooling circuit.
The object of the invention is to provide a cooling system and a method of cooling a generator, i.e., the stator and/or the rotor of the generator, which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this kind, and which is simple and cost-effective.
With the above and other objects in view there is provided, in accordance with the invention, a cooling system for cooling a generator, comprising:
a cooling circuit having oxidation-resistant cooling channels in a stator and/or rotor of a generator conducting coolant for cooling the generator;
a compensating container communicating with the cooling circuit for the coolant in the cooling circuit; and
a source of fresh coolant communicating with the cooling circuit for feeding fresh coolant and maintaining an electric conductivity of the coolant in the cooling circuit below a predetermined threshold.
In other words, the cooling system for cooling the stator and/or the rotor of a generator has a cooling circuit or coolant loop and a compensating container for a coolant flowing through the cooling circuit. Oxidation-resistant cooling channels are provided in the stator and/or in the rotor, and the electric conductivity of the coolant is bounded above essentially by virtue of the fact that fresh coolant is fed to the cooling circuit.
The following advantages can be achieved by means of oxidation-resistant cooling channels, for example cooling channels made from high-grade steel:
The limits of the oxygen content of the coolant can be generously dimensioned.
It is possible to dispense with nitrogen purging for the purpose of minimizing the oxygen content in the coolant.
The level of the pH value is of subordinate importance.
An ion exchanger can be eliminated.
The substantial outlay on time for the purpose of conditioning the water during commissioning of the generator is eliminated.
The invention is based on the finding that it is possible to dispense with chemical filters or ion exchangers in the case of a cooling system having oxidation-resistant cooling channels. A low electric conductivity of the coolant is achieved in a simple and cost-effective way by feeding deionized fresh coolant. By contrast with cooling channels made from, for example, copper, in the case of oxidation-resistant cooling channels there is no need to observe a rigorously closed coolant loop.
In accordance with an added feature of the invention, the compensating container is integrated into a parallel section connected in parallel with the cooling circuit.
The compensating container is preferably integrated into a parallel section connected in parallel with the cooling circuit. As set forth above, in the case of water-cooled generators a compensating container has frequently been arranged such that the entire coolant flows through it. This requires a compensating container of very large dimensions. Such a compensating container is a substantial cost factor. Alternatively, a compensating container has been connected to the cooling circuit via a spur line. In the case of such a design, the stagnates in the compensating container and becomes enriched with ions. The integration of the compensating container into a shunt section parallel to the cooling circuit renders it possible, on the one hand, to design the compensating container to be small. On the other hand, coolant flows continuously through, with the result the coolant the latter does not stagnate. Consequently, there is no substantial increase in conductivity, as a result of which it is possible, in turn, to set a limitation on conductivity particularly effectively by feeding fresh coolant.
The compensating container preferably holds between 50 and 800 l, in particular between 100 and 300 l. It is also preferably possible to guide a primary coolant flow through the cooling circuit and to guide a secondary coolant flow through the parallel section, the primary coolant flow being larger by a factor of 10 to 1000, in particular by a factor of 50 to 200, than the secondary coolant flow. The primary coolant flow is preferably between 10 and 100 m3/h, in particular between 20 and 40 m3/h. The secondary coolant flow is preferably between 10 and 500 l/h, in particular between 100 and 250 l/h.
The compensating container is preferably connected to a discharge line which serves to discharge surplus coolant from the cooling circuit. It is thereby possible for surplus coolant to be discharged simply via a discharge line, whereas previously there was a need to provide an overpressure valve.
It is further preferred for the discharge line to have a U-shaped bend in the region of which a gas outlet opening is arranged such that upon overshooting of a limiting gas pressure in the compensating container gas can be discharged from the compensating container via the gas outlet opening. An overpressure valve can thereby be eliminated. The coolant level can preferably be monitored via a sight glass.
In accordance with an additional feature of the invention, the compensating container is positioned separately from the generator. The compensating container therefore does not form a structural unit with the generator. Such an embodiment is possible owing to the compensating container of smaller dimensions which is arranged outside the cooling circuit. In particular, this results in the advantage that the compensating container does not have to be provided with any expensive vibration damping. Such vibration damping is required when, as previously, the compensating container forms a structural unit with the generator, that is to say, for example, is arranged on the generator. The compensating container is thereby exposed to the vibrations which are caused by the generator during operation.
Preferably provided in the cooling circuit is a calming section which serves for degassing and calming the coolant. Such a calming section can, for example, simply be a line connected in parallel with the cooling circuit. In such a calming section, the coolant flows more slowly and can be degassed. The parallel section in which the compensating container is arranged preferably branches off from this calming section.
In accordance with again an additional feature of the invention, there is integrated a cooler with a coolant inlet in the cooling circuit, the calming section being connected upstream of the coolant inlet. It is preferred to provide two coolers whose coolant inlets are connected by means of the calming section. This configuration exhibits a particularly suitable arrangement of the calming section.
The cooling system is preferably used for cooling the stator of a water-cooled turbo-driven generator, in particular a turbo-driven generator with a power of between 500 and 1300 MVA.
With the above and other objects in view there is also provided, in accordance with the invention, a method of cooling a stator of a generator, which comprises: conducting coolant through oxidation-resistant coolant channels in a generator; and
supplementing the coolant with fresh coolant for maintaining an electric conductivity of the coolant at below a predefined threshold, wherein the fresh coolant has a lower electric conductivity than the coolant.
In other words, the objects with regard to the method are satisfied with the method for cooling the stator and/or the rotor of a generator. The coolant is guided through oxidation-resistant coolant channels of the stator and/or the rotor. The electric conductivity of the coolant is essentially bounded above by supplementing the coolant with fresh coolant, which has a lower electric conductivity than the coolant in the coolant loop.
In accordance with a concomitant feature of the invention, the coolant is degassed and calmed in a calming section, in particular in a calming section connected upstream of the cooler.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a cooling system and a method for cooling a generator, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.